This invention relates to tamper-proof locking mechanisms for controls having a rotatable control shaft projecting outwardly from a body housing a control means and an operating handle extension. In one aspect, the invention relates to tamper-proof locking mechanisms for quarter turn valves having a stem extension, such as ball valves, butterfly valves and plug valves.
Quarter turn valves typically include a valve member rotatably mounted in a valve body, a rotatable shaft or stem connected to the valve member and having an external portion extending outwardly from the valve body and an operating handle connected to the external end portion of the control shaft or stem for moving the valve member between open and closed positions. When this type valve is used in piping systems encased with insulation or situated at a location where it is difficult to reach the operating handle, some kind of extension usually is connected to the external end of the stem in place of the operating handle and the operating handle connected to the outer end of this extension. McAndrew U.S. Pat. No. 4,756,507 discloses an example of such an extension.
In some fluid systems, it is essential that certain manually-operated control valves be maintained in either the full open or full closed position during normal operation. For example, Occupational Safety and Health Administration regulations require that certain control valves in hydraulic and pneumatic systems be positively locked in the open or closed position. Another example is fire protection sprinkler systems where control valves must be full open at all times to insure proper water flow in the event of an emergency.
When such valves are located in areas where there is a risk of intentional tampering or where they can be unintentionally closed, opened or otherwise mispositioned, a locking mechanism which reliably and positively locks the operating handle in a selected position is required. Roberts U.S. Pat. No. 5,014,528 discloses a locking mechanism for quarter turn valves including an operating handle which is connected directly to the external end of the valve stem and is rotated to move the valve member between open and closed positions. The locking mechanism includes a pair of circumferentially-spaced lugs on the exterior of the body at locations corresponding to the open and closed positions. A slider member, mounted on an intermediate portion of the handle for reciprocative movement between locked and unlocked positions, carries a latch element having an opening for receiving the respective one of the lugs when the handle is either in the open or closed position. When the slider member is in a locked position, with the locking element in place, it restrains both rotational movement and axial movement of the handle relative to the stem.
A locking mechanism for valves employing an operating handle extension having the same capability is highly desirable.